This disclosure generally relates to high gain photo and electron multiplier devices and to methods of manufacture thereof. More particularly, this disclosure relates to high-gain position-sensitive photomultiplier devices that are smaller, more robust, and less expensive than other commercially available photomultipliers.
Photomultiplier tubes and microchannel plates are often used for detection of light. Photomultiplier tubes (photomultipliers or PMTs for short), members of a class of vacuum tubes, and more specifically vacuum phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. These detectors multiply the current produced by incident light by as much as several million times, in multiple dynode stages, enabling (for example) individual photons to be detected when the incident flux of light is very low.
The combination of high gain, low noise, high frequency response or, equivalently, ultra-fast response, and large area of collection has earned photomultiplier tubes an essential place in nuclear and particle physics, astronomy, medical diagnostics including blood tests, medical imaging, motion picture film scanning (telecine), radar jamming, and high-end image scanners known as drum scanners. Elements of photomultiplier technology, when integrated differently, are the basis of night vision devices.
Currently, photomultiplier tubes are the most common choice for scintillator photon detection because of cost and gain linearity. Unfortunately, they are bulky, heavy, and fragile.
Micro-channel plate (MCP) detectors are a planar component used for detection of particles (electrons or ions) and impinging radiation (ultraviolet radiation and X-rays). They are closely related to photomultiplier tubes, as both intensify single particles or photons by the multiplication of electrons via secondary electron emission. However, because a microchannel plate detector has many separate channels, it can additionally provide spatial resolution.
A micro-channel plate is a slab made from highly resistive material of typically 2 millimeter thickness with a regular array of tiny tubes or slots (microchannels) leading from one face to the opposite, densely distributed over the whole surface. The microchannels are approximately 10 micrometers in diameter (6 micrometer in high resolution MCPs) and spaced apart by approximately 15 micrometers; they are parallel to each other and often enter the plate at a small angle to the surface (about 8° from normal).
Photomultiplier tubes are more common than microchannel plates in scintillator-based detection systems because they are significantly less expensive and have a larger dynamic range where the gain is linear. Microchannel plates offer modest amplification and size advantages, but are significantly more expensive and are at least as fragile as photomultiplier tubes. Fabrication of microchannel plates requires sophisticated glass fiber-bundle drawing techniques and results in both high cost per unit and very fragile final structures. Due to the fragility of the microchannel plates itself, packaged devices are also bulky because of the more severe constraints placed on the packaging to protect the microchannel plates.
Since microchannel plates are expensive and bulky and since photomultiplier tubes are heavy, bulky and fragile, it is desirable to find replacements that are inexpensive, light, flexible and can detect single photons.